Tilt angle automatic compensator in all directions

ABSTRACT

A tilt angle automatic compensator used for a device requiring verticality or horizontality is disclosed. The automatic compensator comprises a container 4 where a transparent liquid to form free liquid surface 1 is sealed, a light projection system for projecting light beam toward the free liquid surface at a predetermined angle so that it is totally reflected on the free liquid surface, and an optical system arranged at a predetermined position along optical path of the totally reflected light beam after passing through the container with sealed liquid and for equalizing change of reflection angle of optical axis corresponding to change of incident angle of optical axis in all directions. When the liquid container is tilted and incident angle of the light beam is relatively changed with respect to the free liquid surface, sensitivity varying according to the direction of change of reflection angle is optically compensated.

FIELD OF THE INVENTION

The present invention relates to a tilt angle automatic compensator usedin survey instrument, a measuring instrument, etc. for measuring changesof tilting or for maintaining the optical axis of the instrument in avertical direction.

BACKGROUND OF THE INVENTION

When a survey instrument, a measuring instrument, etc. are used forsurveying purpose, it is necessary to make compensation for tilting ofthe reference plane of the survey instrument or the measuring instrumentor to compensate deviations from the verticality of an optical axis.

In the past, compensation has been automatically performed as follows: Apendulum such as a lens or a prism is suspended by 2 or 3 suspensionlines. When main unit of the survey instrument or the measuringinstrument is tilted, the pendulum is braked by a braking mechanism suchas a magnetic braking mechanism to automatically compensate opticalpath.

As one of the methods to detect tilting of reference plane of main unitof the measuring instruments, reflection on a free liquid surface isutilized.

In this method, a light beam is projected onto the free liquid surface,and any change in the optical axis of the reflected light is detected bya photodetector. When mercury is used as a liquid having free liquidsurface and the light beam is projected perpendicularly to the freeliquid surface, it is possible to obtain reflection angle of the samesensitivity to tilting of the liquid surface in all 2-dimensionaldirections, and tilting of the reference plane can be detected.

However, the liquid such as mercury as described above is not verypractical to use in terms of both cost and safety, and transparentliquid such as silicone oil is used in practical application. When thetransparent liquid is used, total reflection is utilized for thepurpose. Because of critical angle between liquid and air, in order toachieve total reflection of light beam on liquid surface, it isnecessary to project the light beam onto the free liquid surface at anincident angle θ to match the above critical angle. In conventional typetilt detecting device utilizing the free liquid surface, the light beamis irradiated to the free liquid surface at a predetermined angle.

When a light beam is irradiated to the free liquid surface at apredetermined angle, the change of reflection angle of the reflectedlight relating to different biaxial directions to the tilting of theliquid surface is not uniform. Therefore, in the tilting detectingdevice utilizing a free liquid surface, measures must be taken to takeinto account the non-uniform change of reflection angle in biaxialdirections. For this reason, light beams with two different optical axesare projected at a predetermined angle to the free liquid surface, andthe reflected light beams are received by photodetectors. Lightreceiving position in only one direction is detected by eachphotodetector, and by the change of the light receiving positions of thephotodetectors, tilting to the two optical axes is detected. From thetilting of the two optical axes thus detected, tilting of referenceplanes of survey instrument, measuring instrument, etc. to horizontalplane are calculated, and compensation is performed based on the resultsof the calculation.

In the former example of the conventional type device described above,however, a pendulum is suspended and this leads to more complicatedstructure. Also, the suspension of the pendulum during assembling of thedevice is not easy, and adjustment is also not simple. Further, thechange over time of suspension lines causes change in its length, and itis very difficult to maintain the accuracy. Because a special brakingdevice is required for braking the pendulum, this also makes thestructure more complicated. Further, suspension structure of thependulum is very delicate and is susceptible to shock.

In the latter example of the conventional type device, utilizing totalreflection on a free liquid surface, assembling and adjustment aresimple, and there is no change over time because no suspension line isused. Because the liquid is used in closed condition, the device hashigh shock-resistance and high resistance to environmental conditions.Because liquid is used, braking can be performed by utilizing viscosityof the liquid, and no braking device is required. Thus, the problems inthe vertical direction tilting automatic compensator using a pendulumhave been overcome by the latter device.

However, because light beams with two different optical axes areirradiated to the free liquid surface at predetermined angles,projection system of light beams is divided into two optical systems,and this leads to the more complicated arrangement of the device.

To solve the above problems, the compensator of the present inventiondetects tilting of reference plane or performs automatic compensation ofvertical line by monoaxial optical system only, utilizing totalreflection of free liquid surface.

DISCLOSURE OF THE INVENTION

The automatic compensator according to the present invention basicallycomprises a container where a transparent liquid to form a free liquidsurface is sealed, a light projection system for projecting a light beamtoward the free liquid surface at a predetermined angle so that it istotally reflected from the free liquid surface along an optical path,and an optical system, arranged at a predetermined position along theoptical path of the totally reflected light beam after passing throughthe container with sealed liquid, for equalizing in all directionschange of the reflection angle of the reflected beam corresponding to achange of incident angle of the incident beam.

Because of the above arrangement, even when the free liquid surface istilted to the incident light toward any direction, compensation is madeto equalize the change of incident angle and the change of reflectionangle. Thus, tilting angle of the entire arrangement can beautomatically compensated according to the change of reflection angle,and this can be utilized for automatic compensation of surveyinstruments and other instruments and devices.

Because the compensator comprises a container with transparent liquidsealed therein to form free liquid surface, a light projection systemfor projecting light beam to the free liquid surface at a given angle sothat total reflection occurs on the free liquid surface, a mirror forreflecting the light beam reflected on the free liquid surface invertical direction, and an optical system arranged at a predeterminedposition of optical path of the reflected light beam and equalizingchange of reflection angle of an optical axis corresponding to change ofincident angle of an optical axis in all directions and for offsettingangular change of the reflected axis optical corresponding to incidentangle change of optical axis. Accordingly, even when the incident angleof light beam to the free liquid surface is relatively changed, angularchange of the reflection is light beam optically offset, and the lightbeam directed in vertical direction is always maintained in verticaldirection and the vertical light beam is utilized as reference insurveying.

It is possible to form a horizontal reference line or a horizontalreference plane by a horizontal light beam when a light path convertingmeans to irradiate vertical light beam in horizontal direction isprovided and when the optical path converting means is rotated.

If a telescope system is arranged on incident light side, it can be usedas a vertical device. Further, if a mirror reflecting the reflectedlight beam in vertical direction is used as a half-mirror and movingrange of the light beam passing through the half-mirror is detected by aphotodetector, it is possible to judge that the tilting of the entiresurvey instrument is within the limitation.

Further, in order that temperature distribution does not occur in theliquid to form the total reflection surface as the condition of usechanges, the liquid is maintained in flat configuration and a heattransfer plate to promote thermal dispersion of the liquid is provided.In addition, a heat insulating layer to suppress heat transfer tooutside is formed. As a result, non-uniformity of refractive index doesnot occur in the liquid, and refraction of optical axis is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing for explaining the changes of reflection angle of areflected light beam when a free liquid surface is tilted;

FIG. 2 is a drawing for explaining changes of reflection angle of areflection light beam when a free liquid surface is tilted;

FIG. 3 is a drawing for explaining a basic configuration of a firstembodiment of the present invention;

FIG. 4 (A) and FIG. 4 (B) each is a drawing for explaining changes of anoptical axis of transmitted light beam to a cylindrical lens system inthe first embodiment of the invention;

FIG. 5 (A) and FIG. 5 (B) each is a drawing for explaining changes of anoptical axis of transmitted light beam to a cylindrical lens system;

FIG. 6 is a drawing for explaining a basic configuration of a secondembodiment of the present invention;

FIG. 7 (A) and FIG. 7 (B) each is a drawing for explaining changes of anoptical axis of transmitted light beam to a toric lens expander in thesecond embodiment;

FIG. 8 is a drawing for explaining an application example of the presentinvention;

FIG. 9 is a drawing for explaining another application example of thepresent invention;

FIG. 10 is a drawing for explaining still another application example ofthe present invention;

FIG. 11 is a drawing for explaining relationship between a beam spot anda pinhole in still another application example;

FIG. 12 shows a basic configuration of a third embodiment of the presentinvention;

FIG. 13 is a drawing for explaining changes of optical axis transmittedlight beam to an anamorphic prism system in the third embodiment;

FIG. 14 (A) and FIG. 14 (B) each is a drawing for explaining changes ofoptical axis of transmitted light beam to the anamorphic prism system;

FIG. 15 is a drawing for explaining an application example relating tothe third embodiment of the present invention;

FIG. 16 is a drawing for explaining another application example relatingto the third embodiment of the present invention;

FIG. 17 is a drawing for explaining still another application examplerelating to the third embodiment of the present invention:

FIG. 18 is a drawing for explaining relationship between a beam spot anda pinhole in still another application example of the invention.

FIG. 19 is a front cross-sectional view of a concrete example of aliquid container;

FIG. 20 is an arrow diagram along the line A--A of FIG. 19; and

FIG. 21 is a front cross-sectional view of another concrete example ofthe liquid container.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, detailed description will be given on the presentinvention in connection with the drawing attached herewith:

FIG. 1 is a diagram showing various relationships between the incidentlight beam and the free liquid surface from which it is totallyreflected.

First, referring to FIG. 1 and FIG. 2, when a light beam is irradiatedto a free liquid surface at a predetermined angle and the light beam istotally reflected on the free liquid surface, and if the free liquidsurface is relatively tilted with respect to the light beam, thesensitivity of the change of reflection angle with respect to thetilting direction of the liquid surface differs.

In fact, the free liquid surface maintained horizontally and it is theincident direction of the light beam which is changed. However, thefollowing description will be given under the assumption that theincident direction of the light beam is constant and the free liquidsurface is tilted.

In the figure, reference numeral 1 represents a free liquid surface, andit is supposed that an incident light beam 2 enters the free liquidsurface 1 at an angle θ. It is assumed that the free liquid surface 1 isapproximately aligned a plane in x-z coordinate formed by coordinateaxis x and coordinate axis z and that the coordinate axis perpendicularto the coordinate plane is y. It is also assumed that an optical axis ofthe incident light beam 2 is present in a coordinate plane formed by thecoordinate axes z and y. When the free liquid surface is tilted aroundthe coordinate axis x by an angle α, an optical axis of reflected lightbeam 3 moves to the reflected light beam 3' in the y-z coordinate plane,and reflection angle is changed by ξ1x within the x-y coordinate plane.In this case, the relation between liquid surface displacement angle αand reflection displacement angle ξ1x is expressed by ξ1x=2α, and areflection displacement angle ξ2x within x-y coordinate plane does notoccur. In the figure, reference numeral 14 represents a mirror.

In contrast, if the free liquid surface 1 is tilted around thecoordinate axis z by an angle α as shown in FIG. 2, the reflected lightbeam 3 is separated from the x-y coordinate plane and the y-z coordinateplane. Therefore, reflection displacement angle ξ1z and reflectiondisplacement angle ξ2z appear respectively on the x-y coordinate planeand -the y-z coordinate plane. Further, the relation between thereflection displacement angle ξ1z and the liquid surface displacementangle a of the free liquid surface 1 is given by:

    ξ1z=cos.sup.-1 (cos.sup.2 θcos 2α+sin.sup.2 θ)

    ξ2z=π/2-cos.sup.-1 (1-cos 2α) sin θcos θ) (1)

For instance, if it is supposed that α=10' and θ=50°, ξ2z=1.7", thevalue ξ2z is negligible in terms of accuracy. Further, if it is supposedthat refractive index of the liquid is optical axis after light beam haspassed through the liquid is given by:

    ξ1x'=2nα

    ν1z'=n·cos.sup.-1 (cos.sup.2 θcos 2α+sin.sup.2 θ)                                                  (2)

Therefore, sensitivity to the liquid surface displacement angle αdiffers in the reflection displacement angle ξ1x' and the reflectiondisplacement angle ξ1z'. In the present invention, the difference of thesensitivities of the displacement angle in the reflection displacementangle ξ1x' and the reflection displacement angle ξ1z' is compensated andequalized by optical means. As a result, an optical axis is obtained,which exhibits angular change always at a constant rate with respect toall directions.

Now, description will be given on a first embodiment of the presentinvention, referring to FIG. 3.

In the figure, reference numeral 4 represents a container with liquidsealed in it and provided on main unit of a device such as a surveyinstrument, and a free liquid surface 1 is formed by the liquid sealedin the container 4. To the free liquid surface 1, a light beam emittedfrom a light source 6 is irradiated at a given angle through acollimator lens 5 so that total reflection occurs, and an optical axisof the light beam is located in y-z coordinate plane as described above.

Under the condition where the free liquid surface 1 is not tilted, acylindrical lens system 9 having a pair of cylindrical lenses 7 and 8and a reflection mirror 14 are arranged along an optical axis of thereflected light beam 3 totally reflected on the free liquid surface 1.Each of the cylindrical lenses 7 and 8 has curvature in only onedirection. The cylindrical lens 7 is a convex cylindrical lens havingfocal length f1, and the cylindrical lens 8 is a concave cylindricallens having focal length f2.

The light beam passing through the cylindrical lens system 9 isreflected by the reflection mirror 14 in vertical direction, and thelight beam reflected by the reflection mirror 14 passes through a beamexpander 12, which comprises convex lenses 10 and 11. Here, if it issupposed that focal length of the convex lens 10 is f3 and focal lengthof the convex lens 11 is f4, the distance between the convex lens 10 andthe convex lens 11 is set to: f3+f4.

The cylindrical lens system 9 may be arranged along an optical pathafter reflected by the reflection mirror 14.

In the following, description will be given on the operating principle.

First, in case a light beam enters from the direction of radius ofcurvature of the cylindrical lens 7 as shown in FIG. 4 (A), the relationof the angles formed by the reflected light beam 3 and the optical axisof the cylindrical lens 7, i.e. incident angle a and exit angle a' fromthe cylindrical lens 8 is given by:

    a'=(f1/f2) a                                               (3)

Also, in case light beam enters from a plane including generating lineof curved surface of the cylindrical lens 7 as shown in FIG. 4 (B), therelation of the angles formed by the reflected light beam 3 and theoptical axis of the cylindrical lens 7, i.e. incident angle α, and exitangle a' from the cylindrical lens 8 is given by:

    a=a'                                                       (4)

Here, to the moving of the reflected light beam 3 in case the freeliquid surface I is tilted around z-axis, the cylindrical lens system 9is arranged as shown in FIG. 4 (A), and to the moving of the reflectedlight beam 3 in case the free liquid surface 1 is tilted around x-axis,the cylindrical lens system 9 is arranged as shown in FIG. 4 (B).

If it is supposed in FIG. 3 that the setting incident angle θ to theliquid is 50°, tilt angle of the device, i.e. tilt angle α of the freeliquid surface 1 is 10', and refractive index n of the liquid is 1.4,the reflection displacement angle ξ1x' in case the free liquid surface 1is tilted around x-axis and the reflection displacement angle ξ1z' incase the free liquid surface 1 is tilted around z-axis are given by theequation (2) as ξ1x'=28' and ξ1z'=18' respectively. Therefore, thedifference of sensitivity between the reflection displacement angle ξ1x'and the reflection displacement angle ξ1z' is: (ξ1x'/ξ1z')=1.555 times.

Accordingly, under this condition, there exist the following relations:

    ξ1x'=2nα; ξ1z'=1.286nα                   (5)

Therefore, if (f1/f2)=2/1.286 from the equation (2), the displacementangle ξ1z' of optical axis transmitted through the cylindrical lenssystem 9 is converted to: 1.286 nα×2/1.286=2 nα, and after passingthrough the cylindrical lens system 9, ξ1x'=ξ1z'. Thus, even when thefree liquid surface 1 is tilted to any direction, reflectiondisplacement angle of the same sensitivity can be obtained to thetilting. Thus, the tilting of the free liquid surface, i.e. tilting ofthe entire device, can be obtained based on of reflection displacementangles.

Further, in case light beam passing through the cylindrical lens system9 and being reflected upward by the reflection mirror 14 passes throughthe beam expander 12, and if angular magnification of the beam expander12 is 1/2 n times, optical axis after transmitting is tilted by:

    (ξ1x'=ξ1z'=2nα)×1/2n=α             (6)

The final optical axis after passing through the beam expander 12 runsalways perpendicularly to the free liquid surface 1 , i.e. it ismaintained in vertical direction. If it is supposed that focal length ofthe convex lens 10 is f3and focal length of the convex lens 11 is f4,angular magnification of the expander 12 is f3/f4. By selecting f3 andf4, angular magnification can be set to 1/2 n.

Next, with respect to the embodiment shown in FIG. 3, the cylindricallens system 9 may be rotated by 90° to obtain:

    (f2/f1)=1.555

    (f3/f4)=1/1.286n                                           (7)

The description will be given on the relation of entering and exit ofthe reflected light beam 3 in case the cylindrical lens system 9 isrotated by 90°, referring to FIGS. 5 (A) and (B).

As described above, if it is supposed that the tilt angle of the freeliquid surface 1 is α, the setting incident angle of a light beam is θ,and refractive index of the liquid is n, the reflection displacementangles of the optical axis of the reflected light beam 3 with respect tothe free liquid surface 1 are as follows:

ξ1x'=2 nα when the free liquid surface 1 is tilted around x-axis; and

ξ1z'=1,286 nα when the free liquid surface 1 is tilted around z-axis.

After the light beam passes through the cylindrical lens system 9, thereflection displacement angle ξ1x' is given by:

    ξ1x'=2nα×1/1.555=1.286nα              (8)

and the reflection displacement angle ξ1z' is maintained as passingthrough the cylindrical lens system 9 as:

    ξ1z'=1.286nα                                      (9)

Further, because angular magnification of the beam expander 12 isf3/f4=1/1.286 as described above,

    (ξ1x'=ξ1z')×(f3/f4)=1.286nα/1.286n=α(10)

As described above, an optical axis can be maintained always in verticaldirection.

Description will be given now on a second embodiment of the invention,referring to FIG. 6.

In this embodiment, the combination of the cylindrical lens system 9 andthe beam expander 12 shown in FIG. 3 is replaced by an expander 13comprising a set of a toric lenses 15 and 16. The toric lenses 15 and 16are the lenses, which have different x-direction focal point andz-direction focal point. If it is supposed that x-direction focal pointsare f1x and f2x respectively, and z-direction focal points are f1z andf2z respectively, and further, if it is supposed that

    f1x/f2x=1/1.286n

    f1z/f2z=1/2n                                               (11).

it is possible to set the exit angle from the toric lens 16 to α asshown in FIGS. 7 (A) and (B), and the optical axis can be maintainedalways in vertical direction.

As described above, it is possible according to the present invention tomaintain an optical axis of an exit light beam always in verticaldirection regardless of tilting of the reflecting plane and to utilizethe exit light beam as vertical reference line. In the following,description will be given on application examples of the presentinvention.

FIG. 8 shows a pentagonal prism or a pentagonal mirror 17 rotatablyarranged along an optical axis of light beam emitted from the beamexpander 12. The exit light beam is emitted horizontally by thepentagonal mirror 17, and horizontal reference plane by the exit lightcan be formed by rotating the pentagonal mirror 17. Specifically, thepresent invention can be applied as a levelling device.

FIG. 9 shows another application example.

In this application example, a telescope system 18 is arranged on lightsource side of the first embodiment shown in FIG. 3. With sucharrangement, this can be used as a vertical device.

When the system is used practically with the above arrangement, tiltingof the entire system is usually limited. Therefore, it is necessary todetect whether it is within the required limit of tilting before use.Such requirement can be met by adding the following arrangement.

Referring now to FIG. 10, instead of the reflection mirror 14 asdescribed above, a half-mirror 40 is disposed, and the reflected lightbeam from the free liquid surface 1 is split into a reflected light beam41 in vertical direction and a transmitted light beam 42. Thetransmitted light beam 42 passes through a convex lens 43 and through apinhole 45 formed on a shielding plate 44 and is received by aphotodetector 46. The pinhole 45 is arranged at focal point of theconvex lens 43. Also, a diameter of the pinhole 45 is to be in sizecorresponding to the range of limitation.

When the entire system is tilted, an optical axis of the light beamreflected from the free liquid surface 1 is deviated. Because thecylindrical lens system 9 is included in this system as described above,the reflected light beam exhibits uniform sensitivity to tilt angle ofthe entire system in all directions. The transmitted light beam 42passes through the convex lens 43 and the pinhole 45 and is received bythe photodector 46. The pinhole 45 and the photodetector 46 are arrangedat the focal point of the convex lens 43. If it is supposed that focallength of the convex lens 43 is f0, the optical axis moves by f0· tan ξ0on the pinhole 45 with respect to the reflection displacement angle ξ0.

When this movement exceeds the required limit of tilting, the diameterof the pinhole 45 is determined so that light quantity received by thephotodetector 46 is below the required light quantity.

By monitoring the light quantity received by the photodetector 46, it ispossible to judge whether tilting of the entire system is within thelimited angle.

For example, if it is supposed that incident angle θ to the free liquidsurface 1 is 50°, limited tilt angle α of the entire system is 10',refractive index n of the liquid is 1.4, focal length f0 of the convexlens 43 is 100 mm, and pinhole diameter is then the deviation of anoptical axis after passing through the cylindrical lens system 9 is:ξ0=2 n α. Therefore, the movement 1 of optical axis of the pinhole 45(position of focal point of the convex lens 43) is given by:

    1=f0· tan ξ0=100×tan (2×1.4×10/60)=0.81 (12)

In case the pinhole 45 has an opening of this diameter and when a beamspot of the transmitted light beam 42 moves by 0.81 as shown FIG. 11, itis over outer diameter of the pinhole 45, and the received lightquantity of the shielding plate 44 decreases. Accordingly, by stoppinglight emission from the light source 6 when the decreased light quantityis detected, the present invention can be used only within the requiredlimit.

The pinhole 45 may be omitted and a photodetector such as CCD may beused as the photodetector 46, and the position of the beam spot isdetected by the photodetector 46.

In FIG. 12, a third embodiment of the present invention shown. Theembodiment of FIG. 12 uses an anamorphic prism system 33 instead of thecylindrical lens system 9 with the configuration shown in FIG. 3.

With the free liquid surface I not tilted, an anamorphic prism system 33comprising a pair of wedge-like prisms 34 and 35 is arranged along theoptical axis of the reflected light beam 3 totally reflected by the freeliquid surface 1.

The light beam passing through the anamorphic prism system 33 isreflected by a reflection mirror 14 in vertical direction, and the lightbeam reflected by the reflection mirror 14 is passed through the beamexpander, which comprises convex lenses 10 and 11. If it is supposedthat focal length of the convex lens 10 is f3 and focal length of theconvex lens 11 is f4, the distance between the convex lenses 10 and 11is set to: f3+f4.

The anamorphic prism system 33 may be arranged along the optical pathafter reflected by the reflection mirror 14. In FIG. 12, if it issupposed that the setting incident angle θ to the liquid is 50°, tiltangle of the device, i.e. tilt angle α of the free liquid surface 1 is10', and refractive index n of the liquid is 1.4, by the equation (2)obtained by referring to FIG. 1, the reflection displacement angle ξ1x'in case the free liquid surface 1 is tilted around x-axis and thereflection displacement angle ξ1z' in case the free liquid surface 1 istilted around z-axis are ξ1x'=28' and ξ1z'=18' respectively. Therefore,the difference of sensitivity between reflection displacement angle ξ1x'and the reflection displacement angle ξ1z' is (ξ1x'/ξ1z')=1.555. Underthis condition, therefore,

    ξ1x'=2nα;ξ1z'=1.286nα                    (13)

The anamorphic prism system 33 optically compensates the difference ofsensitivity.

Here, description is given on the anamorphic prism system 33, referringto FIG. 13 and FIGS. 14(A) and 14(B).

If it is supposed that apex angles of the wedge-like prisms 34 and 35 ofthe anamorphic prism system 33 are a34 and a35 respectively, relativeangle of the wedge-like prisms and 35 is b, refractive index is ng,incident light beam is Din and exit light beam is Dout:

    Magnification M=(Din/Pout)=cos.sup.2 ·sin.sup.2 a) (14)

Thus, the angular magnification is approximately 1/M. Therefore, if theprism apex angles a34 and a35, relative angle b of the wedge-like prisms34 and 35, and the refractive index ng are selected in such manner thatthe following relation exists:

    M=2nα/1.286nα=1.555                            (15)

(e.g. if ng=1.51, a34 and a35=27.732°, and b=44.793°), then ξ1x' afterpassing through the anamorphic prism system 33 is converted to: 2nα×1.286 nα/2 nα=1.286 nα, and ξ1x'=ξ1z' after passing through theanamorphic prism system 33.

An optical axis of the reflected light beam 3 after passing through theanamorphic prism system 33 always has uniform reflection displacementangle with respect to tilting of the free liquid surface 1 in alldirections. Thus, even when the free liquid surface 1 is tilted in anydirection, it is always possible to obtain the reflection displacementangle with the same sensitivity with respect to the tilting.

Further, when the light beam passing through the anamorphic prism system33 and being reflected upward by the reflection mirror 14 passes throughthe beam expander 12 and if angular magnification of the beam expander12 is 1/1.286 n, the optical axis after passing through the beamexpander is tilted by:

    (ξ1x'=ξ1z'=1.286nα)×1/1.286n=α     (16).

and the final optical axis after passing through the beam expander 12runs always perpendicularly to the free liquid surface 1, i.e. always invertical direction. If it is supposed that focal length of the convexlens 10 of the beam expander 12 is f3 and focal length of the convexlens 11 is f4, angular magnification of the expander 12 is f3/f4. Byselecting the values of f3 and f4, angular magnification can be set to1/1.286 n.

Next, in the embodiment shown in FIG. 12, the anamorphic prism system 33may be rotated by 90°, and the prism apex angles a34 and a35 of thewedge-like prisms 34 and 35, relative angle b of the wedge-like prisms34 and 35 and refractive index ng may be properly selected in suchmanner that the value of M is 1/1.555.

The anamorphic prisms system 33 in the above optical system is generallyutilized to form the beam of elliptical shape into circular shape. Forexample, in case laser diode is used as the light source,cross-sectional shape of the light beam can be made closer to circularshape by the anamorphic prism system 33. (Beam shape of laser diode isin elliptical shape.)

In general, the devices used in combination with such laser diode haveoften the functions as a laser pointer or a laser marker, and it isdesirable that the shape of irradiated beam is closer to circular shape.Therefore, the utilization of the anamorphic prism system 33 forcorrection of an optical axis is very effective for obtaining the beamof circular shape.

As described above, it is possible according to the present invention tomaintain the optical axis of exit light beam always in verticaldirection. In the following, description will be given on an applicationexample related to the third embodiment of FIG. 12.

FIG. 15 shows a pentagonal prism or a pentagonal mirror 17 rotatablyarranged along the optical axis of light beam emitted from the beamexpander 12. The exit light beam is emitted horizontally by thepentagonal mirror 17, and by rotating the pentagonal mirror 17, it ispossible to form a horizontal reference plane by the exit light beam.Specifically, the present invention can be applied for a levellingdevice.

FIG. 16 shows still another application example.

In this application example, a telescope system 18 is arranged on thelight source side of the third embodiment of FIG. 12. With sucharrangement, this can be utilized as a vertical device just as theapplication example of FIG. 9.

When the system is practically used with the above arrangement, tiltingof the entire system is usually limited. Thus, it is necessary to detectthat the system is within the required limit of tilting when it is used.To meet the requirements, the same measure as given in FIG. 10 may betaken. This will be described below, referring to FIG. 17.

Instead of the reflection mirror 14 as described above, a half-mirror 40is disposed, and the reflected light beam from the free liquid surface 1is split into a reflected light beam 41 in vertical direction and atransmitted light beam 42. The transmitted light beam 42 passes througha convex lens 43 and through a pinhole 45 formed on a shielding plate 44and is received by a photodetector 46. The pinhole is arranged at focalpoint of the convex lens 43. Also, a diameter of the pinhole 45 is to bein size corresponding to the range of limitation.

When the entire system is tilted, the optical axis of the light beamreflected from the free liquid surface 1 is deviated. Because theanamorphic prism system 33 is included in this system as describedabove, the reflected light beam exhibits uniform sensitivity to tiltangle of the entire system in all directions. The transmitted light beam42 passes through the convex lens 43 and the pinhole 45 and is receivedby the photodector 46. The pinhole 45 and the photodetector 46 arrangedat the focal point of the convex lens 43. If it is supposed that focallength of the convex lens 43 is f0, the optical axis move by f0·tan ξ0on the pinhole 45 with respect to the reflection displacement angle ξ0.

When this movement exceeds the required limit of tilting, the diameterof the pinhole 45 is determined so that light quantity received by thephotodetector 46 is below the required light quantity.

By monitoring the light quantity received by the photodetector 46, it ispossible to judge whether tilting of the entire system is within thelimited angle.

For example, if it is supposed that incident angle θ to the free liquidsurface 1 is 50 °, limited tilt angle α of the entire system is 10',refractive index n of the liquid is 1.4, focal length f0 of the convexlens 43 is 100 mm, and pinhole diameter is R, then the deviation ofoptical axis after passing through the anamorphic prism system 33 is: ξ0=1.286 n α. Therefore, the movement 1 of optical axis of the pinhole 45(position of focal point of the convex lens 43 is given by:

    1=f0·tan ξ0=100×tan (1.286×1.4×10/60)=0.52 (17)

In case the pinhole 45 has an opening of this diameter and when beamspot of the transmitted light beam 42 moves by 0.52 mm as shown in FIG.18, it is over outer diameter of the pinhole 45, and the received lightquantity of the shielding plate 44 decreases. Accordingly, by stoppinglight emission from the light source 6 when the decreased light quantityis detected, the present invention can be used only within the requiredlimit.

Next, description will be given on an example of the container 4 withsealed liquid referring to FIG. 19 and FIG. 20.

The container 4 with sealed liquid is fixed on main unit of the devicetogether with other lens systems or it is constituted as a part of thedevice. In this case, if the device is used under environmentalcondition where there occurs temperature difference, e.g., in case thedevice is brought outdoors from inside the building, temperaturedistribution occurs within the liquid sealed in the container Oncetemperature distribution occurs in the liquid, refractive index alsoshows a distribution to match such temperature distribution, andrefraction of optical axis occurs within the liquid. The example of thecontainer 4 with sealed liquid given in FIG. 19 and FIG. 20 is useful tosolve such problems.

Detailed description is as follows:

Inside an outer case 20 in inverted trapezoid shape, an inner case 21 ina shape similar to the outer case 20 in provided. Along upper surface ofthe inner case 21, a space 22 in planar shape is formed, and a lightentering path 23 and a light exit path 24 communicated with the space 22are provided. Axial center of the light entering path 23 is aligned withoptical axis of the incident light beam, and axial center of the lightexit path 24 is aligned with optical axis of the reflected light beamwhen the free liquid surface 1 is horizontal.

On bottom surface of the space 22, a heat transfer plate 25 is fixed.The heat transfer plate 25 is provided with a window hole 26 at itscenter so that an incident light beam and reflected light beam can gothrough. On each of upper ends of the light entering path 23 and thelight exit path 24, a transparent glass cock 27 is fixed, andtransparent liquid 28 is tightly sealed by the cock 27. Sealing quantityof the transparent liquid 28 is determined so that free liquid surfaceis formed.

The inner case 21 is accommodated in the outer case 20, and apredetermined surrounding space 29 is formed around the inner case 21.Glass windows 30 and 31 are arranged at the positions where axialcenters of the light entering path 23 and the light exit path 24 of theouter case 20 pass through. The outer case 20 is designed in airtightconstruction, and the surrounding space 29 is kept in vacuum conditionor gas is sealed in it.

Further, the outer case 20 and the inner case 21 are made of a materialhaving lower thermal conductivity such as synthetic resin in order tominimize heat radiation and heat absorption to and from outside.

As described above, the space 22 where the transparent liquid 28 issealed is designed in thin planar shape and a heat transfer plate 25 isprovided on the bottom surface of the space. As a result, heatpropagation speed is increased and the property to keep uniformtemperature is increased when temperature change occurs in thetransparent liquid 28. The surrounding space 29 serves as a heatinsulating layer to the heat transfer to and from the inner case 21.Thus, temperature change or temperature change speed of the transparentliquid 28 is suppressed.

The occurrence of temperature distribution difference within thetransparent liquid 28 is suppressed, and this prevents the refraction ofoptical axis of the light beam and the change of cross-sectional shapeof the light beam caused by the change of refractive index. As a result,stability to temperature change of environment increases, and measuringaccuracy is raised.

Next, FIG. 21 shows another example of the container 4 with sealedliquid. Without forming the surrounding space 29 around the inner case21, the inner case 21 is enclosed by the outer case 20 made ofheat-insulating material, and heat insulating layer is formed around theinner case 21 by the outer case 20.

It is needless to say that the shape of the container 4 with sealedliquid is not limited to the above examples.

INDUSTRIAL APPLICABILITY

As described above, the tilt angle automatic compensator according tothe present invention is useful as a vertical device or as a levellingdevice to provide a reference line by reflected light beam and areference plane by scanning the reflected light beam, in case ofmeasuring a tilt of device, in case of being equiped for a surveyinstrument required horizontality and verticality or in case ofcompensating tilt angle of the survey instrument.

What we claim are:
 1. A tilt angle automatic compensator, comprising acontainer where a transparent liquid to form a free liquid surface issealed, a light projection system for projecting a light beam toward thefree liquid surface at a predetermined angle so that it is totallyreflected from the free liquid surface along an optical path, and anoptical system, arranged at a predetermined position along the opticalpath of the totally reflected light beam after passing through thecontainer with sealed liquid, for equalizing in all directions change ofthe reflection angle of the reflected beam corresponding to change ofincident angle of the incident beam.
 2. A tilt angle automaticcompensator according to claim 1, wherein the optical system comprises aconvex cylindrical lens and a concave cylindrical lens.
 3. A tilt angleautomatic compensator according to claim 1, wherein the optical systemcomprises an anamorphic prism system.
 4. A tilt angle automaticcompensator, comprising a container where a transparent liquid to form afree liquid surface is sealed, a light projection system for projectinga light beam toward the free liquid surface at a predetermined angle sothat it is totally reflected from the free liquid surface along a firstoptical path, a mirror for re-reflecting in a vertical direction along asecond optical path the light beam reflected from the free liquidsurface, a first optical system, arranged at a predetermined positionalong said first optical path, for equalizing in all directions changeof the reflection angle of the reflected beam corresponding to change ofincident angle of the incident beam and a second optical system,arranged at a predetermined position along said second optical path, foroffsetting angular change of the re-reflected beam corresponding tochange of incident angle of the incident beam.
 5. A tilt angle automaticcompensator according to claim 4, wherein the first optical systemcomprises a convex cylindrical lens and a concave cylindrical lens andwherein the second optical system comprises a beam expander.
 6. A tiltangle automatic compensator according to claim 4, wherein the secondoptical system comprises a set of toric lenses.
 7. A tilt angleautomatic compensator according to claim 4, wherein the first opticalsystem comprises an anamorphic prism system and the second opticalsystem comprises a beam expander.
 8. A tilt angle automatic compensatoraccording to claim 4, wherein there is provided an optical pathconverting means for receiving the light beam traveling in a verticaldirection and for emitting a light beam in horizontal direction.
 9. Atilt angle automatic compensator according to claims 1 or 4, wherein atelescope system is arranged on incident light beam side entering thefree liquid surface.
 10. A tilt angle automatic compensator according toclaim 4, wherein the mirror for re-reflecting the light beam in avertical direction is provided as a half-mirror, the light beam passingthrough the half-mirror is received by a photodetector, and moving ofoptical axis of the light beam transmitted through the half-mirror isdetected by the photodetector.
 11. A tilt angle automatic compensatoraccording to claims 1 or 4, wherein a transparent liquid is sealed in aspace of planar shape.
 12. A tilt angle automatic compensator accordingto claim 11, wherein a heat transfer plate is provided at bottom surfaceof the space of planar shape.
 13. A tilt angle automatic compensatoraccording claims 1 or 4, wherein a heat insulating layer is formedaround an inner case where the transparent liquid is sealed.